1. Field of the Invention
The present invention relates to the structure of a cylinder block constituting an engine.
2. Related Art
A cylinder block is one of media which transmit the explosive power to a crank system, and the most important structural member which must support the inertia load etc. of the crank system. Moreover, the structure of the cylinder block influences size, weight, whole durability, noise, etc. of the engine.
Conventionally, an art for increasing thickness of a cylinder portion is mainly applied as an art for improving the rigidity of the cylinder block which constructs an engine.
For example, in the Japanese Patent Laid Open Gazette 2001-221098, a large range portion such as a portion from the same side with a crankcase to the center in the cylinder block is constructed thickly so that the art for improving the rigidity of the cylinder block is disclosed. The art for improving the rigidity of the cylinder block is disclosed also in the Japanese Patent Laid Open Gazette Hei. 6-213064, where many portions of the cylinder block are constructed thickly.
However, when the cylinder block is formed thickly in a wide range thereof, the weight of the engine increases. Conversely, when the cylinder block is formed thinly for weight saving, the rigidity of the cylinder block is reduced, thereby increasing the noise of the engine.
Therefore, it is desired that the noise and weight of the engine are decreased while the rigidity of the cylinder block is enhanced.
A cooling-water gallery is constructed in the cylinder block so as to surround a cylinder, and cooling-water flows in the cooling-water gallery so that the cylinder is cooled. A drain hole of the cooling-water gallery is formed in the cylinder block and open on the side surface of the cylinder block. However, the drain hole is not disposed in the bottom of the cooling-water gallery. The cooling-water gallery of the cylinder block is disposed higher than a lubricating-oil gallery considering its arrangement relationship with the lubricating-oil gallery constructed within the cylinder block.
However, as disclosed, for example in the Japanese Patent Laid Open Gazette 2001-152851, only cooling of the cylinder like the temperature control of the cylinder wall is considered for the cooling-water gallery constructed in the conventional cylinder block. The cooling of lubricating-oil etc. circulating in the cylinder block is not considered especially. Moreover, since the drain hole of the cooling-water gallery is constructed higher than the bottom thereof, it is difficult to drain cooling-water completely. In case cooling-water remains within the cooling-water gallery for a long time, there is the possibility that degradation of the cylinder block might occur.
Furthermore, in the cylinder block formed by casting, the periphery of a hole formed by a member supporting a core is tapered, and a plug is installed in the hole.
In case the plug is installed in the hole after the hole is tapered by the member supporting the core, there is the possibility of change in the installing position of the plug according to the casting state of the cylinder block, so the labor and time are required in order to improve the precision of installing the plug.